mkosi-sandbox1

Usage

Overview

mkosi-sandbox runs the given command in a custom sandbox. The sandbox is configured by specifying command line options that configure individual parts of the sandbox.

If no command is specified, mkosi-sandbox will start bash in the sandbox.

Note that this sandbox is not designed to be a security boundary. Its intended purpose is to allow running commands in an isolated environment so they are not affected by the host system.

It is possible to use mkosi-sandbox to create an in process sandbox for python applications by importing it as a module and invoking its enter function with only options. No command line to execute is needed in this case. As an example:

import mkosi.sandbox
mkosi.sandbox.enter(["--become-root"])
print(os.getuid())

Only the enter function can be invoked. Invoking any other functions from mkosi.sandbox is not supported and may break in future versions.

Options

--tmpfs DST

Mounts a new tmpfs at DST in the sandbox.

--dev DST

Sets up a private /dev at DST in the sandbox. This private /dev will only contain the basic device nodes required for a functioning sandbox (e.g. /dev/null) and no actual devices.

--dir DST

Creates a directory and all missing parent directories at DST in the sandbox. All directories are created with mode 755 unless the path ends with /tmp or /var/tmp in which case it is created with mode 1777.

--bind SRC DST

The source path SRC is recursively bind mounted to DST in the sandbox. The mountpoint is created in the sandbox if it does not yet exist. Any missing parent directories in the sandbox are created as well. The source path may optionally be prefixed with a + character. If so, the source path is interpreted relative to the sandbox root directory instead of the host root directory.

--bind-try SRC DST

Like --bind, but doesn’t fail if the source path doesn’t exist.

--ro-bind SRC DST

Like --bind, but does a recursive readonly bind mount.

--ro-bind-try SRC DST

Like --bind-try, but does a recursive readonly bind mount.

--bind-foreign SRC DST

Like --bind, but mkosi-sandbox will allocate a user namespace and provision it with a transient UID range using systemd-nsresourced and then idmap the foreign UID range to this transient UID range using systemd-mountfsd for each --bind-foreign mount. Finally, mkosi-sandbox will join the user namespace just before executing the configure command in the sandbox.

Using this option requires systemd-nsresourced and systemd-mountfsd v260 or newer.

--ro-bind-foreign SRC DST

Like --bind-foreign, but does a readonly mount.

--bind-nofollow SRC DST

Like --bind, but does not follow symlinks for SRC. If SRC is itself a symlink, the symlink is bind mounted as-is rather than its target.

--ro-bind-nofollow SRC DST

Like --bind-nofollow, but does a readonly mount.

--symlink SRC DST

Creates a symlink at DST in the sandbox pointing to SRC. If DST already exists and is a file or symlink, a temporary symlink is created and mounted on top of DST.

--write DATA DST

Writes the string from DATA to DST in the sandbox.

--overlay-lowerdir DIR

Adds DIR from the host as a new lower directory for the next overlayfs mount.

--overlay-upperdir DIR

Sets the upper directory for the next overlayfs mount to DIR from the host. If set to tmpfs, the upperdir and workdir will be subdirectories of a fresh tmpfs mount.

--overlay-workdir DIR

Sets the working directory for the next overlayfs mount to DIR from the host.

--overlay DST

Mounts a new overlay filesystem at DST in the sandbox. The lower directories, upper directory and working directory are specified using the --overlay-lowerdir, --overlay-upperdir and --overlay-workdir options respectively. After each --overlay option is parsed, the other overlay options are reset.

--unsetenv NAME

Unsets the NAME environment variable in the sandbox.

--setenv NAME VALUE

Sets the NAME environment variable to VALUE in the sandbox

--chdir DIR

Changes the working directory to DIR in the sandbox.

--same-dir

Changes to the working directory in the sandbox to the current working directory that mkosi-sandbox is invoked in on the host.

--become-root

Maps the current user to the root user in the sandbox. If this option is not specified, the current user is mapped to itself in the sandbox. Regardless of whether this option is specified or not, the current user will have a full set of ambient capabilities in the sandbox. This includes CAP_SYS_ADMIN which means that the invoked process in the sandbox will be able to do bind mounts and other operations.

If mkosi-sandbox is invoked as the root user, this option won’t do anything.

--map-foreign

Map the foreign UID range in the sandbox. For more information on the foreign UID range, see Users, Groups, UIDs and GIDs on systemd Systems ⟨https://systemd.io/UIDS-GIDS/⟩\c .

When running mkosi-sandbox unprivileged, this option requires systemd-nsresourced v260 or newer.

--map-delegate N

Map N additional 64K UID/GID ranges in the sandbox.

This is needed to execute systemd-nspawn or any program that tries to allocate a transient UID range via systemd-nsresourced from within the mkosi-sandbox environment. This option requires systemd-nsresourced v260 or newer.

--suppress-chown

Specifying this option causes all calls to chown() or similar system calls to become a noop in the sandbox. This is primarily useful when invoking package managers in the sandbox which might try to chown() files to different users or groups which would fail unless mkosi-sandbox is invoked by a privileged user.

--suppress-sync

Specifying this option causes all calls to sync() or similar system calls to become a noop in the sandbox. This is primarily useful when invoking package managers in the sandbox which might try to sync() files when extracting packages which is unnecessary when building images and slows down execution time significantly.

--unshare-net

Specifying this option makes mkosi-sandbox unshare a network namespace if possible.

--unshare-ipc

Specifying this option makes mkosi-sandbox unshare an IPC namespace if possible.

--pack-fds

Pack inherited file descriptors together starting at file descriptor number 3 and set $LISTEN_FDS to the number of packed file descriptors and $LISTEN_PID to the current process pid.

--debug

Log various messages describing how the sandbox is set up.

--version

Show package version.

--help, -h

Show brief usage information.

Examples

Start bash in the current working directory in its own network namespace as the current user.

mkosi-sandbox --bind / / --same-dir --unshare-net

Run id as the root user in a sandbox with only /usr from the host plus the necessary symlinks to be able to run commands.

mkosi-sandbox \
    --ro-bind /usr /usr \
    --symlink usr/bin /bin \
    --symlink usr/lib /lib \
    --symlink usr/lib64 /lib64 \
    --symlink usr/sbin /sbin \
    --dev /dev \
    --bind /proc /proc \
    --tmpfs /tmp \
    --become-root \
    id